Caption: Coloured scanning electron micrograph (SEM) of Bordetella pertussis, Gram-negative, aerobic, non-motile, coccobacillus prokaryote (bacterium). Bordetella pertussis causes whooping cough or pertussis. This bacterium occurs in the human host. The bacterium is spread by coughing and by nasal drops. The incubation period is 7-14 days. A vaccine is available for this bacterial pathogen. Pertussis vaccine is part of the DTaP (diphtheria, tetanus, acellular pertussis) immunization. Bordetella parapertussis causes a less severe case of human whooping cough but can also cause pneumonia in sheep. B. pertussis also produces a lymphocytosis-promoting factor, which causes a decrease in the entry of lymphocytes into lymph nodes. This can lead to a condition known as lymphocytosis. Magnification: x5,000 when shortest axis printed at 25 millimetres.